This application claims the priority of German Patent Document 100 02 506.4, filed Jan. 21, 2000, and German Patent Document 100 29 301.8, filed Jun. 14, 2000, the disclosures of which are expressly incorporated by reference herein.
The present invention relates to an air-permeable transport belt drivable by a drive roller for transporting a fiber strand to be condensed over a sliding surface of a condensing zone of a spinning machine, said sliding surface comprising a suction sit.
For the condensing of a fiber strand leaving a drafting unit of a spinning machine it is important that the fiber strand is transported in the condensing zone disposed on an air-permeable transport element and still in a twist-free state and having fibers lying essentially parallel to one another, and that in the condensing zone an air stream is generated which flows through the transporting element, which air stream, depending on its width and/or direction influences the degree of condensing and which positions the fibers transversely to the transport direction and thus bundles or condenses the fiber strand. In the case of a fiber strand condensed in this way, a spinning triangle does not occur when twist is being imparted, so that the thread produced is more even, more tear-resistan, and less hairy.
The transport element plays a special role in condensing. In German published patent application DE 198 46 268 (corresponding U.S. Pat. No. 6,108,873), a transport element in the form of a perforated transport belt is described. This transport belt is designed as a circulating loop and slides on its inner side over a stationary sliding surface. The transport belt is driven on its outer side by means of friction.
The transport belt should be air-permeable where it guides the fiber strand, namely in the effective condensing area. The lateral areas of the transport belt, which do not run over the suction slit, do not necessarily need to be air-permeable. Their function is reliable transport by means of friction. On the other hand, the transport belt has to be in a position to slide over the sliding surface without any great friction.
It is an object of the present invention to design a transport belt of the above mentioned type so that it fulfills the requirements in relation to a friction drive and to sliding over a stationary sliding surface and at the same time functions reliably in the actual condensing area.
This object has been achieved in accordance with the present invention in that the transport belt comprises at least one area arranged to contact the drive roller, which area differs from an area arranged to contact the sliding surface and from an area arranged to contact the fiber strand in relation to its surface structure.
A transport belt of this type is designed differently over its effective width as well as in relation to its outer side and inner side, so that a type of zone belt is formed. In the air-permeable area, a good friction transport is not necessary, it is sufficient when the fiber strand to be condensed is transported reliably, which is already ensured by the air-permeability of the transport belt. Outside of the actual condensing area, in particular in the edge areas of the transport belt, the surface structure of the transport belt is designed for a good friction transport. At the same time, however, good sliding ability of the circulating transport belt is ensured as against the stationary sliding surface. The apparatus operating with the transport belt functions particularly well when the differences in friction between the drive roller and the transport belt on the one hand, and between the transport belt and the sliding surface on the other hand, are as large as possible. These friction pairings must be favorably influenced by relevant factors. The coefficient of friction between the transport belt and the sliding surface can be minimized by means of favorable surface coatings on the sliding surface and favorable designs of the transport belt. Advantageous is, for example, a sliding surface, which is slightly fluted in the direction of motion of the transport belt and has a roughness of 3 to 7 xcexcm.
In the simplest embodiment, the area of the transport belt arranged to contact the sliding surface can, in relation to its surface structure, correspond to that area arranged to contact the fiber strand. In a further embodiment, it is, however, a contemplated to further optimize the transport belt in that the area arranged to contact the sliding surface can, with regard to its surface structure, also differ from the area arranged to contact the fiber strand.
With regard to the form, various types of transport belt are contemplated:
In one embodiment it is provided that the area arranged to contact the drive roller as well as the area arranged to contact the fiber strand are each placed on the outer side of the transport belt in the form of a circulating loop. This is, for example, for a transport belt according to the above mentioned prior art, when the transport belt loops on its inner side a suction channel comprising the sliding surface and is driven by a drive roller on its outer side.
In a further variation it can be provided that the area arranged to contact the drive roller and also the area arranged to contact the sliding surface is placed on the inner side of the transport belt in the form of a circulating loop. Such an embodiment is then practical when, for example, the transport belt hoops a drive roller.
For purely practical reasons, it is, as a rule, useful when the actual condensing area is located somewhat centrally to the transport belt. It is hereby sufficient when the transport belt is air-permeable only over a width corresponding to the width of the suction slit. In one embodiment of the present invention it is then provided that the at least one area arranged to contact the drive roller is an edge area of the transport belt.
In order to achieve a friction take along of the transport belt by means of the drive roller, a kind of positive engagement should be aimed for. For this reason it is provided in a further embodiment of the present invention that the at least one area arranged to contact the drive roller comprises a rough textured surface.
Because of the necessity of keeping the transport belt clean, there is a certain interest in designing the area arranged to contact the drive roller as narrow as possible in comparison to the other areas. The remaining area arranged to contact the fiber strand is less susceptible to fiber fly, particular when it is provided with a finely textured surface instead of a roughly patterned one. The area of the transport belt guiding the fiber strand may even be completely without any kind of textured surface, which is then the case when the air-permeable area of the transport belt is not perforated, but is simply porous.
The friction drive of the transport belt by means of the drive roller can be improved by the following measures:
The transport belt is thermally formed on the surface in such a way What a kind of fluting or the like occurs, with which, in connection with the resilience of the roller covering of the driving roller, a kind of positive engagement arises.
The transport belt is alternatively provided on both sides with an additional surface, which has a higher coefficient of friction, for example, a rubber coating.
The drive roller can also obtain special friction coatings, which are, for example, more resilient on the sides of the drive roller than in the center and/or which are somewhat enlarged in diameter. Thus the edge areas would be pressed somewhat harder against the transport belt.